Below is an email (in the email it is HTML so it looks nicer) that is sent out when a request for Google Classroom is approved. Fred or G Suite Admin has to approve request so they may come much later than the request is submitted. The email looks fake but is a legit email.
From: Classroom Teachers
Date: Tue, Feb 4, 2020 at 3:46 PM
Subject: Your request to join Classroom Teachers was approved
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Congratulations, your request to join the Classroom Teachers group was approved by a group moderator.
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